Polymorphonuclear neutrophils can recognize, engulf and kill microorganisms. The initial encounter between the microbe and the neutrophil takes place at the neutrophil surface and usually at the leading edge as the cells advance. We examined the topography of receptors for concanavalin A on neutrophils that were polarized in a chemotactic gradient and on neutrophils that were unpolarized. We found that polarized neutrophils clustered receptors for Concanavalin A at the leading stage. When these receptors were bound they migrated to the tail of the cell and new unbound receptors were then arrayed at the front of the cell, ready to function. We feel that the array of the receptors at the leading edge of the neutrophil may be important for the cell's ability to function as an efficient phagocyte. We are continuing studies to characterize the position of other receptors on the neutrophil and to better understand the factors that are involved in controlling receptor topography.